Amplifier circuits



Dec. 19, 1933. HAHNLE 1,940,414

AMPLIFIER CIRCUITS Filed Feb. 19. 1952 2 Sheets-Sheet 1 INVENTOR WALTERHAHNLE ATTORNEY Dec. 19, 1933. v HAHNLE 1,940,414

AMPLIFIER C IRCUITS Filed Feb. 19, 1932 2 Sheets-Sheet. 2

If: W1 W2 INVENTOR WALTER HAHNLE BY W 7W ATTORNEY Patented Dec. 19, 1933UNITED STATES PATENT OFFICE AMPLIFIER CIRCUITS Application February 19,1932, Serial No. 594,055, 7

and in Germany January 9, 1931 4 Claims.

I have filed an application in Germany, January 9, 1931.

The invention is concerned with a circuit scheme designed to compensatenon-linear distortions, and the same is primarily applicable toamplifiers intended to supply more than the average power. What wasexpected of amplifier arrangements of the earlier art is that theyshould combinefreedom from non-linear distortion with a maximum poweroutput. This demand means poor utilization of the amplifier tubes, forthe utilization is limited by the desired freedom from distortion.

In order to compensate such distortion as is ascribable to the knee inthe characteristic curve, the idea has been practiced in the prior artto provide transfer elements, say, amplifier tubes, whose characteristiccurve presented a contrary curvature or knee. However, schemes of thiskind suffer from a fundamental drawback. They necessitate a very exactbalancing of the characteristic curves of the tubes, and as a resultthey are highly sensitive to the replacing of circuit elements, mostparticularly of tubes. is that with known circuit schemes stray ordisturbing waves (line noises or hums) due, for example, to foreignsources of trouble which are not known' beforehand and which may ariseonly temporarily, can not be readily compensated.

According to this invention, for the purpose of avoiding the saiddisadvantages, a basically different way is followed. What is used iswhat may be termed a linearizing scheme presenting a linearcharacteristic (say, an amplifier of low power) which is so controlledby the circuit arrangements' to be freed from distortion and is socombined or connected therewith that the aggregation of currents orpotentials furnished from the said linearizing scheme and thearrangements to be freed from distortion, will be free of all nonlineardistortions. In these circuit schemes it is not necessary to knowexactly the characteristic of the part causative of the distortion inorder to proportion accordingly the characteristic of the linearizingscheme; in fact, it is sufiicient for the linearizing means to present alinear form of characteristic. 1

By the coupling provided between the linearizing arrangement and therest of the circuit arrangement the linearizing scheme, as it were,automatically adapts itself to the form of the characteristic of thepart to be freed from distortion. Especially in the case of poweramplifiers the invention makes it feasible to choose generators ofmaximum efliciency for the power Another point stages regardless of thequestion of distortion. As a result the circuit elements may be reducedto a minimum amount.

The invention is not only useful for amplifier arrangements, butgenerally wherever a compensation of non-linear distortions is required.The invention is suited for measuring arrangements just as readily asfor the purpose'of absorbing disturbing frequencies, especially inschemes in which the currents or grid potentials are improperly filteredor where the filament circuits are dissymmetric. Inside the scope ofthis invention it is immaterial in what particular way the non-lineardistortions have been caused, i. e., whether it has been'th'e curvatureor knee of a tube characteristic or the knee in an iron-cored couplingmeans or that of a load-dependent resistance that is responsible forthis condition. The invention insures freedom from undesired frequenciesboth in alternating current potentials as well as direct currentpotentials.

Fundamentally speaking there exist two ways and means of uniting thelinearizing means with the distorting circuit arrangement. That is tosay, the linearizing means and the distorting arrangement are eitherconnected in parallel with the consuming device or load, or else thelinearizing means, the distorting arrangement and the consumer areconnected in series.

In the drawings, which will be used in the further explanation of myinvention,

- Fig. l is a generalized analysis of one form of the invention, r

Fig. 2 is a generalized analysis of another form of the invention,

Fig. 3ris a curve showing the relation between certain elements of thenetwork of Fig. 1,

Fig. 4 is a circuit diagram embodying the invention of Fig. 1,

Fig. 5 is a circuit diagram embodying the invention of Fig. 2.

In order to explain the basic idea of the invention there shall first bediscussed the parallel scheme which is important in practice. For adiscussion of the principle we shall regard the distorting arrangementand the linearizing means each as a generator connected conjointly withthe consumer or load. Referring to Fig. 1, I denotes the distortinggenerator briefiy to be called the power generator, and III denotes thelinearizing generator, both being connected in parallel relation to theconsumer or load Z. The assumption shall be made that the impedance ofthe consumer Z involves any complexity at all and that it is linear. Theinternal impedance R1 of the power generator shall not be constant, butalways positive, in other words, generator I constantly delivers power.Owing to the change in the resistance R1 with the load, non-lineardistortions are produced. The object of the linearizing means is torender the aggregate current (J1+J3) flowing through the consumer Zindependent of the alterations of the said resistance R1. The saidaggregate current, in fact, should be a function only of the potentialto be amplifled, the control potential Egl, and the properties of thelinearizing generator III whose characteristic curve is presupposed tobe linear. If the current J1 delivered by the power generator is toosmall then the linearizing generator must furnish a correspondinglylarger current J3. In other words, the generator III acts both as agenerator as well as a consumer according to whether the internalresistance of generator I fluctuates upwards or downwards.

To explain the calculations hereinbelow made, this is a list of thesymbols used:

Eo1=separately controlled electromotive force of generator IEos=separately controlled electromotive force of generator III (In allschemes E01=Eoa E1, J1, R1 terminal potential, current and internalresistance of generator I E3, J3, R3 terminal potential, current andinternal resistance of generator III A1=arbitrary constant=amplification factor (gain) of generator In (for all frequencies andamplitudes real and constant).

The terminal potential of the power generator I is where J1-R1 is theinternal drop of potential of the generator.

The linearizing generator is so connected that the following potentialsprevail at its grid:

Whence a value for the terminal potential of the generator III is:

The first three members of Equation (5') correspond to the abovementioned grid potentials Egl, Egfl and Eg3, whereas the last termrepresents the internal fall of potential of the linearizing generator.The portion EgZ of the terminal potential due to the grid potential, aswill be noted, is equal and opposite to the internal drop of potentialof the tube.

What follows from Equation (5) is:

The integral current (J 1+J 3) flowing through the consumer Z, as willbe seen, is a function only of the control potential, the terminalpotential of generator III and the constant factor A1. In other words,the influence of the variable resistance- R1 is eliminated by a circuitscheme as here disclosed.

The operation and eifect of the linearizing means can be explained alsoby the aid of the following equations: From Equation (1) there follows:

From Equation (6) this value is derived for the current of thelinearizing generator:

Equation (7) introduced in Equation (8) and when putting E1=E3 for aparallel circuit scheme results in:

What may be seen from the last two equations is that the current of thelinearizing generator comprises a component adapted to compensate thedefect in the generator current J1. From Equation (10) there resultsfurthermore that the current J3 will be so much smaller the less thedifference between A1 and R1. This fact is important so far as thedimensioning of the linearizing factor is concerned. By suitableproportioning of the factor A1 it is feasible to make conditions so thatthe linearizing generator furnishes almost as much current as isrequired for the purpose of compensating the distortions occasioned bythe changes in the resistance R1.

The relation between J1 and J3 flows from the Equations (6) and (1):

Fig. 3 shows the generator current J1 and the integral current J1+J3as'a function of the potential E01E:. The distance between the twocurves measured in the direction of the ordinate axis, corresponds to oris a criterion for the current J; to be supplied by the linearizinggenerator. The constant angle of inclination of the line (J1+J3) isequal to A1, whereas the variable angle of inclination of the curve J1corresponds to the resistance R1.

For the series scheme shown in Fig. 2 for the two generators I and IIIthere result similar relations as for the parallel scheme. The twoschemes are reciprocal as to resistance. In what follows the samesymbols are used as in the calculations covering the parallelconnection. The terminal potential of the power generator I is again:

, E1=E01*-]1'R1 In order to compensate the undesirable dependence uponR1 the terminal potential E3 of the linearizing generator III is inseries with the terminal potential E1, the former containing the valueE1 as a negative term. In this manner perfect linearizing would befeasible if, similarly as in the parallel connection scheme, back-feedor regeneration is provided so that the internal potential fall of thelinearizing generator will play no part whatever. However, the generatorIII would have to furnish a very large power, not to mention this factthat entirely unstablev conditions would arise.

Now, in order to avoid this drawback the genprevail these threepotentials:

Hence, there results a terminal potential for the line arisinggeneratoras follows:

M rtha-A141+ R3-J1R3-J1 (17) where the first four terms represent thecomponent ascribable to the three grid potentials, and the last termrepresents the internal falloff of the potential of the linearizinggenerator.

The factor of the regeneration term proportional to J1 has been sochosen that the internal fall off of potential of generator III doesnot, appear at all. From Equation (17) there follows for the sum totalof the two terminal potentials con- The aggregate potentialfed to theconsumer Z, as will thus be noted, is independent of theproperties ofthe generator I. From Equations (13) and (17) there results 1 1 Acomparison of Equations (20) and (13) goes to show in what way theinfluence of R1 is compensated by the series connection of E1 and E3.

Introducing the Equation (13) into Equation (18) there is obtained thereresults, similarly as for the parallel connection scheme, that theterminal potential of the linearizing generator becomes so, much lower,the smaller the difference between A1 and R1.

As stated at the outset the present linearizing scheme is adapted tocompensate also foreign disturbing waves, which, therefore are notcontained in the input potential E 1. In the calculations thesedisturbing frequencies need not be taken into consideration inasmuch asthey would produce similar eifects as the distortions occasioned byalterations of the resistance R1. The same things that hold true of thecalculations and the considerations made in connection therewith, applyalso to the construction of the circuit arrangements, for also in thelatter those disturbing frequencies need not be specially taken intoaccount. The linearizing scheme compensates automatically alldisturbances which arise within the power circuit arrangement betweenthe input and the output ends thereof.

Now, Figs. 4 and 5 illustrate two embodiments of the basic idea of theinvention by way of exways and means.

ample. Fig. 4 shows the power'and linearizing generator connected inparallel, while 5 i1- lustrates the series arrangement thereof.

In the case shown in Fig. 4 the power stage is represented by the twoamplifier tubes V1 and V2 connected push-pull fashion. However, thelinearizing scheme is not confined to the combination of such apush-pull stage, indeed, it may be used in combination with any'other'circuit arrangement. Before the linearizing generator V4 anamplifier tube'vs is coupled by way'of resistances and capacities,though this is-not'essential for the linearizing'generator, in fact,the-same is merely provided so as to insure proper phase relations, thelatter being insurable also 'by other Across the input terminals K1 andK2 is connected the primary winding W1 of an input transformer which hastwo secondary windings W2 and W3. By way of the secondary winding W; theinput potential E 1 is fed t'o'the grids of the two amplifler'tubes V1and V2. The same potential E is applied also by way of the secondsecondary winding W2 to the grid of the amplifier tubevs. Included inthe plate circuit of the power generator are the primary windings of thetwo transformers Trl and T12 and the ohmic resistances X and the chokecoils Dr. Connected with the series-connected; secondary windings of thetwo transformers is the consumer or load device Z. The output circuit ofthe linearizing generator V4 is connected in parallel with the outputend of'the'power transformer by way of the transformer Tr4. In parallelwith the series connection comprising the resistances X and the chokecoils Dr is the primary winding of the transformer T73 whose secondarywinding conjointly with the. second secondary winding W2 of the inputtransformer is connected in series with the grid of the amplifier tubeV3. The

' potential Eg3 transferred by the transformer T1'3 is proportional tothe aggregate current (Ji-i-Ja) flowing through the resistances X andthe choke coils Dr.

In the plate circuit of the linearizing generator V4, and in series withthe primary winding of the transformer T14 there is included a seriesarrangement R comprising an ohmic resistance and a choke-coil. Across Ris produced a fall of potential which is proportional to the platecurrent J 3 of the linearizing generator. This fall of potential E 2 byway of the condenser C1 is applied also to the grid circuit of theamplifier tube V3. The choke-coils Dr connected in series with the gridand plate batteries serve for precluding the alternating currents whichare to flow by way of the condensers C1, C2 and C3. The inductance coilsDr and the inductance pertaining to series arrangement R are necessaryinasmuch as the transformers are not ideal. Some details of the circuitscheme which are not directly related to the linearizing arrangementhave been omitted for the sake of simplicity. For the same reason adistinct battery is shown for each plate and grid circuit.

The elements forming part of the series scheme circuit of the amplifiertube V; connected before the linearizing generator V4. The platecircuits of the'power generator and the linearizing generator includethe two transformers I171 and Ir2 Whose secondary windings arranged inseries supply the consumer device Z.

Assuming that ideal transformers are concerned the currents flowing inthe plate circuits of the two tubes V1 and V4 are alike. Consequentlyalso the-fall of potential across the resistance R. contained in theplate circuit of the linearizing generator is proportional to theconsumer current Ji=J3. In parallel relation to the resistance R'is theprimary Winding of a transformer IT3 whose secondary winding isconnected in series with'the winding W2 of the input transformer in thegrid circuit of the amplifier tube V3. Hence, by way of the transformerIr3 a grid potential Eg3 is applied'to the input circuit of thelinearizing scheme, said potential being proportional to the current inthe consumer circuit.

The third grid potential EgZ which is proportional to the terminalpotential of the power generator is fed by way of the condenser C1 tothe grid circuit of the amplifier tube V3. In the embodiment shown byway of example the said potential is tapped inthe primary winding of thetransformer Irl, it being, of course, feasible to obtain this potentialalso in some other manmer. In lieu of the. condenser C1 also a high ohmresistance could be used under certain circumstances. The choke coils Drand the condensers C2 and C3 have the same denotation and purpose as inFig. 4.

What I'claim is:

1. A distortionless amplification system comprising an electrondischarge device amplifier having an input circuit and an outputcircuit,

means for inductively feeding waves to be amplified through the inputcircuit of said amplifier, a load circuit, means for inductively feedingamplified waves in the output circuit of said amplifier to said loadcircuit, an auxiliary electron discharge device amplification systemhaving an input circuit and an output circuit, means inductivelycoupling the input circuit of said auxiliary amplifier to the input andoutput of said first mentioned amplifier, the coupling being so chosenthat for a desired ratio of amplification of said first mentionedamplifier substantially no currents are fed to the input circuit of saidauxiliary amplifier, and means for inductively coupling the output ofsaid auxiliary amplifier to said load circuit whereby departure fromsaid desired ratio causes currents to be fed into the input circuit ofsaid auxiliary amplifier and causes amplified currents of said auxiliaryamplifier to be fed into said load circuit from the output circuit ofsaid auxiliary amplifier so as to maintain waves in said load circuit ata desired ratio to waves fed to the input circuit of said firstmentioned amplifier.

2. Apparatus as claimed in the preceding claim wherein said firstmentioned amplifier is in the form of a pushpull circuit and whereinneutralization means are provided to prevent oscillation generation ofsaid auxiliary amplifier.

3. Apparatus as claimed in claim 1 wherein the output of said auxiliaryamplifier is parallel with the output of said first mentioned amplifierfor jointly feeding said load circuit.

4. Apparatus as claimed in claim 1 wherein the output of said auxiliaryamplifier and the output of said first mentioned amplifier are seriallyfed into said load circuit.

-WALTER HAHNLE.

